No problem, let's work through this together. We're starting with 8156 and 403 and adding them all up.

Step 1: We'll start by adding the digits 6 & 3 in column 1 and get 9.

Step 2: We'll start by adding the digits 5 & 0 in column 2 and get 5.

Step 3: We'll start by adding the digits 1 & 4 in column 3 and get 5.

Step 4: We'll start by adding the digits 8 & 0 in column 4 and get 8.

So, 8156 + 403 = 8559.

